High-frequency FBG sensor of symmetrical elliptical flexible hinge and monitoring method of high-frequency FBG sensor

Abstract

The invention provides a high-frequency FBG sensor with symmetrical elliptical flexible hinges and a monitoring method of the high-frequency FBG sensor, and relates to the technical field of optical fiber sensing, the sensor comprises a fiber Bragg grating, a base, a first elliptical flexible hinge, a second elliptical flexible hinge, a first mass block and a second mass block; the left side of the base is connected with a first elliptical flexible hinge; the first elliptical flexible hinge is connected with a first mass block; the right side of the base is connected with a second elliptical flexible hinge; the second elliptical flexible hinge is connected with a second mass block; the fiber bragg grating is arranged between the first mass block and the second mass block. As a flexible hinge design, the symmetrical elliptical flexible hinge solves the problem that the motion range is limited, achieves a larger motion range, increases the sensitivity, and keeps high precision at the same time.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and particularly to a high-frequency FBG sensor with a symmetric elliptical flexible hinge and a monitoring method therefor. Background Art

[0002] Common fiber optic vibration sensor structures are mostly cantilever beam type, diaphragm type, and hinge type.

[0003] The prior art is as follows: A miniaturized low-frequency FBG accelerometer based on a symmetric cantilever beam, with a volume of only 6.48 , effectively solving the problems of low sensitivity and excessive volume. However, due to the influence of the cantilever beam characteristics, the natural frequency of the sensor is only 72 Hz. Some researchers proposed to design a fiber optic grating accelerometer based on a diaphragm-type cantilever beam structure. The sensor has a sensitivity of up to 452.6 pm / g in the working direction, and the transverse sensitivity is only 2.16% of the main direction sensitivity, having a strong anti-transverse interference ability. However, due to the limitations of the diaphragm and cantilever beam structures, the frequency response range of the sensor is only 1 - 35 Hz.

[0004] A medium-frequency fiber optic grating accelerometer based on a flexible hinge, using three straight circular flexible hinges to connect two inertial mass blocks and a base into a whole. Then, two FBGs are symmetrically arranged at both ends of the two mass blocks, having temperature self-compensation and a natural frequency as high as 2800 Hz. However, the sensitivity in the flat frequency range is only 21.8 pm / g.

[0005] A two-dimensional cantilever beam vibration sensor based on fiber Bragg grating, which has a high response sensitivity, with sensitivities in the x / y axes being 125.85 pm / g and 82.32 pm / g respectively, having the advantages of multi-directional monitoring and avoiding chirping, etc. However, the flat frequencies of the sensor in the x / y axes are 60 - 150 Hz and 30 - 150 Hz, and the measurable dynamic range is small.

[0006] A new type of miniaturized fiber Bragg grating vibration sensor, which is used for mechanical vibrations in the medium and high frequency ranges with special requirements for size, mass, and distributed measurement. The natural frequency reaches 1525 Hz, but the sensitivity in the 0 - 800 Hz dynamic range is only 12 pm / g. Jianfei Wang et al. developed a new type of temperature and transverse axis insensitive dual fiber Bragg grating vibration sensor using a symmetric counter-twisted structure, effectively eliminating the influence of temperature. However, the natural frequency of the sensor is only 210 Hz, unable to meet the measurement requirements of medium and high frequencies.

[0007] In the above domestic and foreign research, the designs of fiber optic sensors cannot simultaneously take into account the two parameters of natural frequency and sensitivity. Summary of the Invention

[0008] The purpose of the present invention is to provide a high-frequency FBG sensor with a symmetric elliptical flexible hinge and its monitoring method, so as to solve the technical problem that existing optical fiber sensors cannot simultaneously take into account the natural frequency and sensitivity.

[0009] The above object of the present application is achieved through the following technical solutions: The high-frequency FBG sensor includes: An optical fiber Bragg grating, a base, a first elliptical flexible hinge, a second elliptical flexible hinge, a first mass block, and a second mass block; The left side of the base is connected to the first elliptical flexible hinge; the first elliptical flexible hinge is connected to the first mass block; The right side of the base is connected to the second elliptical flexible hinge; the second elliptical flexible hinge is connected to the second mass block; The optical fiber Bragg grating is arranged between the first mass block and the second mass block.

[0010] Optionally, the base is a concave-shaped metal material, and the left side and the right side of the base are symmetric structures; the first elliptical flexible hinge and the second elliptical flexible hinge are arranged in the concave-shaped base.

[0011] Optionally, a first groove is provided in the middle of the upper surface of the first mass block; A second groove is provided in the middle of the upper surface of the second mass block; the first groove is aligned with the second groove; The optical fiber Bragg grating is arranged between the first groove and the second groove by a two-point pasting method.

[0012] Optionally, the base, the first elliptical flexible hinge, the second elliptical flexible hinge, the first mass block, and the second mass block are integrally designed and have a completely symmetric structure on the left and right.

[0013] Optionally, the structural parameters of the first elliptical flexible hinge and the second elliptical flexible hinge are determined by a genetic algorithm; The structural parameters include: the long semi-axis b of the elliptical flexible hinge, the short semi-axis c of the elliptical flexible hinge, and the thickness t of the elliptical flexible hinge.

[0014] A monitoring method based on the high-frequency FBG sensor, which is applied to the transformer application scenario, and the method includes: Collect the vibration signal of the transformer through the high-frequency FBG sensor with a symmetric elliptical flexible hinge; Filter the vibration signal to obtain a filtered spectrogram; Perform time-frequency analysis on the filtered spectrogram to obtain the vibration data of each frequency component; Construct a machine learning model; Obtain a dataset of labeled transformer vibration signals; Train the machine learning model with the dataset of labeled transformer vibration signals; Input the vibration data of each frequency component into the trained machine learning model for classification and identification to determine the operating state of the transformer and complete the monitoring of the transformer.

[0015] An electronic device includes a processor, a memory, a user interface, and a network interface. The memory is used to store instructions. The user interface and the network interface are used to communicate with other devices. The processor is used to execute the instructions stored in the memory so that the electronic device executes a high-frequency FBG sensor for a symmetric elliptical flexible hinge.

[0016] A computer-readable storage medium stores instructions. When the instructions are executed, a high-frequency FBG sensor for a symmetric elliptical flexible hinge is executed.

[0017] The beneficial effects brought by the technical solution provided in this application are: 1. By designing a high-frequency FBG sensor for an integrated symmetric elliptical flexible hinge, the sensor can obtain optimal sensitivity and natural frequency on the premise of meeting the target frequency band; solve the problems of small movement range and low sensitivity of traditional fiber optic vibration sensors. And the sensor is applied to the vibration state monitoring of transformers, realizing the timely detection of equipment, reducing the risk of unexpected equipment shutdown, and improving the overall operation efficiency of the system.

[0018] 2. The method of pasting fiber Bragg gratings at two points effectively solves the chirp phenomenon. Brief Description of the Drawings

[0019] The following will further illustrate this application in conjunction with the drawings. In the drawings: Figure 1 is the structural diagram in the embodiment of this application; Figure 2 is the structural dimension parameter diagram in the embodiment of this application; Figure 3 is the first parameter change diagram in the embodiment of this application; Figure 4 is the second parameter change diagram in the embodiment of this application; Figure 5 is the third parameter change diagram in the embodiment of this application; Figure 6 is the fourth parameter change diagram in the embodiment of this application; Figure 7 is the structural parameter optimization diagram of the elliptical flexible hinge in the embodiment of this application; Figure 8 It is a diagram of the transformer monitoring system in the embodiment of the present application; Figure 9 It is a spectrogram before filtering in the embodiment of the present application; Figure 10 It is a spectrogram after filtering in the embodiment of the present application; Figure 11 It is a time-frequency analysis diagram in the embodiment of the present application; Figure 12 It is a schematic structural diagram of an electronic device in the embodiment of the present application. Specific embodiments

[0020] For a clearer understanding of the technical features, objectives, and effects of the present application, the specific embodiments of the present application will now be described in detail with reference to the accompanying drawings.

[0021] The embodiment of the present application provides a high-frequency FBG sensor with a symmetric elliptical flexible hinge.

[0022] Please refer to Figure 1 , Figure 1 It is a structural diagram of a high-frequency FBG sensor with a symmetric elliptical flexible hinge in the embodiment of the present application. The high-frequency FBG sensor includes: An optical fiber Bragg grating, a base, a first elliptical flexible hinge, a second elliptical flexible hinge, a first mass block, and a second mass block; The left side of the base is connected to the first elliptical flexible hinge; the first elliptical flexible hinge is connected to the first mass block; The right side of the base is connected to the second elliptical flexible hinge; the second elliptical flexible hinge is connected to the second mass block; The optical fiber Bragg grating is arranged between the first mass block and the second mass block.

[0023] As an embodiment, the two hinges are respectively connected to the base and the mass block to form a symmetric-structured fiber optic sensor. The top of the base and the mass block are on the same plane, and the FBG is located between the two mass blocks. This sensor increases the sensitivity simultaneously without affecting the accuracy through the symmetric structure. The structure is simple, the movement range is large, and the method of pasting the optical fiber at two points effectively removes the chirp phenomenon.

[0024] The base is a concave-shaped metal material, and the left side of the base and the right side of the base are symmetric structures; the first elliptical flexible hinge and the second elliptical flexible hinge are arranged in the concave-shaped base.

[0025] A first groove is provided in the middle of the upper surface of the first mass block; A second groove is provided in the middle of the upper surface of the second mass block; the first groove is aligned with the second groove; The fiber Bragg grating is arranged in the middle of the first groove and the second groove by means of two-point pasting.

[0026] As an embodiment, as Figure 1 shown, the high-frequency FBG vibration sensor with a symmetric elliptical flexible hinge is composed of a sensor metal substrate and an FBG (fiber Bragg grating). The metal substrate includes: a base, flexible hinges, and mass blocks. As shown in the figure, 1 and 2 are flexible hinges, 3 is an FBG, 4 and 5 are mass blocks, and 6 is the base. The flexible hinges 1 and 2 are symmetrically distributed on both sides of the base 6, and the cut is elliptical. The mass blocks 4 and 5 are respectively connected to the base 6 through the flexible hinges 1 and 2. There are grooves on the mass blocks, and the optical fiber is placed in the grooves and fixed to the mass blocks through an adhesive. The FBG is suspended in the middle of the two mass blocks.

[0027] The base, the first elliptical flexible hinge, the second elliptical flexible hinge, the first mass block, and the second mass block adopt an integrated design and are completely symmetric in the left-right direction.

[0028] As an embodiment, the entire sensor core is made into an integrated structure. When an external acceleration signal is applied, the two mass blocks move relative to their respective hinges under the action of inertial force, driving the FBG to elongate and contract, causing the central wavelength of the FBG to shift.

[0029] As an embodiment, when the vibration excitation signal acceleration acts in the sensitive direction of the high-frequency FBG sensor with a symmetric elliptical flexible hinge, the two flexible hinges move relative to each other. Due to complete symmetry, the magnitudes of the displacements of the two hinges relative to the center line are always the same; extract one of the hinges for analysis. The length of the FBG (fiber Bragg grating) is , when analyzed individually, half of the length of the FBG is , and the overall sensitivity can be obtained. The structural dimension parameters of the sensor, as Figure 2 shown, the entire system reaches torque balance under the action of inertial force, and the following formula is obtained: , In the formula: is the mass of the mass block; is the distance from the centroid of the mass block to the center of the flexible hinge; is the elastic coefficient of the optical fiber; is the elongation of the optical fiber; is the height of the mass block; is the rotational stiffness of the flexible hinge; is the rotational angle of the hinge. The elastic coefficient of the optical fiber is , In the formula: is the cross-sectional area of the optical fiber; is the elastic modulus of the grating; is the distance between the two optical fiber fixing points on the base and the mass block.

[0030] The centroid of the mass block is , In the formula: is the major semi-axis of the elliptical flexure hinge.

[0031] The rotational stiffness of the elliptical flexure hinge is , , In the formula: is the elastic modulus of the material; is the thickness of the hinge; c is the minor semi-axis of the elliptical flexure hinge, and t is the minimum thickness between the hinges.

[0032] The sensitivity of the sensor is the change in the central wavelength of the fiber grating and the acceleration ratio, that is: , In the formula: is the elasto-optic coefficient; is the central wavelength of the grating; is the fiber strain; is the elongation of the optical fiber.

[0033] Due to the symmetric structure, when the sensor moves in the sensitive direction, both ends of the grating will be stressed and the central wavelength will shift. Therefore, the sensitivity of the sensor is twice that of a single side, 2S.

[0034] Determine the structural parameters of the first elliptical flexure hinge and the second elliptical flexure hinge through the genetic algorithm; The structural parameters include: the major semi-axis b of the elliptical flexure hinge, the minor semi-axis c of the elliptical flexure hinge, and the thickness t of the elliptical flexure hinge.

[0035] As an embodiment, another important feature of the fiber optic vibration sensor is the natural frequency f. Generally speaking, the larger f is, the larger the measurable range of the sensor is.

[0036] The strain potential energy of the optical fiber is , The elastic potential energy of the hinge is , The kinetic energy of the mass block is , From the Lagrangian function , Substitute the Lagrangian function into the Lagrange equation of conservative forces , Substitute the formula to obtain the dynamic equation of the system as , After arrangement, the resonance frequency of the high-frequency FBG sensor is , where the moment of inertia is , It can be seen from the sensitivity formula and the natural frequency formula that the length l of the fiber Bragg grating only affects the sensitivity and has nothing to do with the natural frequency. The shorter the grating length, the higher the sensitivity.

[0037] The indicators affecting the natural frequency include the long semi-axis of the hinge, the length of the mass block, the thickness of the hinge, etc. Select the main indicators, the long semi-axis b, the short semi-axis c and the thickness t of the hinge for analysis.

[0038] Discuss the effects of different long semi-axes b and short semi-axes c on the sensitivity S and the natural frequency f under different hinge thicknesses t, and discuss the effects of different mass block widths e and mass block heights h on the sensitivity S and the natural frequency f under different hinge thicknesses t.

[0039] Such as Figure 3 , Figure 4 , Figure 5 , Figure 6 shown. It can be seen from the analysis that adjusting the sensor parameters will increase the sensor sensitivity and decrease the natural frequency, or decrease the sensitivity and increase the natural frequency. Therefore, it is necessary to optimize the sensor parameters to obtain the optimal sensitivity and natural frequency under the condition of obtaining the target frequency band.

[0040] In order to obtain the optimal sensitivity and natural frequency on the premise of meeting the target frequency band, the genetic algorithm is used to optimize the key parameters b, c and t. The genetic algorithm is a search heuristic algorithm that simulates natural selection and genetic mechanisms. It can optimize multiple parameters. It is necessary to continuously adjust the parameters of the genetic algorithm, such as population size, crossover probability, mutation probability, etc., to observe the influence of these parameter changes on the algorithm performance, and find a more suitable set of parameter settings so that the genetic algorithm can efficiently solve the parameter optimization problem.

[0041] The optimization model is Max S , Parameter optimization, such as Figure 7 shown, considering the possibility of machining accuracy, finally determine b = 0.0031m, c = 0.0016m, t = 0.001m.

[0042] A monitoring method based on high-frequency FBG sensors, applied to the transformer application scenario, the method includes: Collect the vibration signal of the transformer through the high-frequency FBG sensor of the symmetric elliptical flexible hinge; Filter the vibration signal to obtain the filtered spectrogram; Perform time-frequency analysis on the filtered spectrogram to obtain the vibration data of each frequency component; Construct a machine learning model; Obtain a labeled transformer vibration signal dataset; Train the machine learning model through the labeled transformer vibration signal dataset; Input the vibration data of each frequency component into the trained machine learning model for classification and identification to determine the operating state of the transformer and complete the monitoring of the transformer.

[0043] As an embodiment, the designed fiber optic sensor can be used for transformer monitoring. The mechanical vibration frequency range that may be generated during the operation of the transformer is relatively wide. The vibration caused by the cooling system is concentrated in the frequency range below 100 Hz. The steady-state vibration of the transformer body structure (such as windings and iron cores) has a fundamental frequency of 100 Hz and is accompanied by other high-order harmonic components. When a fault or abnormality occurs in the transformer, unusual vibration frequencies may be generated, and problems can be diagnosed through vibration monitoring and analysis. The transformer monitoring system consists of a signal demodulation system composed of a broadband light source, a circulator, a demodulation module, and a PC. The transformer monitoring system is as Figure 8 shown.

[0044] As an embodiment, by filtering the signal collected from the transformer, most of the noise in the original signal is removed, and the main frequency components of the original signal are retained; time-frequency analysis can clearly show each frequency component of the filtered vibration signal; machine learning effectively distinguishes and identifies the vibration spectrum state of the transformer by collecting and processing a large amount of vibration spectrum data, thereby providing reliable technical support for the monitoring and diagnosis of the transformer operating state, timely discovering and warning potential faults, and thus improving the reliability and safety of the transformer.

[0045] As an embodiment, the spectrogram before filtering is as Figure 9 shown, the spectrogram after filtering is as Figure 10 shown, and the time-frequency analysis of the filtered spectrogram is as Figure 11 shown.

[0046] This application also discloses an electronic device. Refer to Figure 12 , Figure 12 which is a schematic structural diagram of an electronic device disclosed in an embodiment of this application. The electronic device 500 may include: at least one processor 501, at least one network interface 504, a user interface 503, a memory 505, and at least one communication bus 502.

[0047] Among them, the communication bus 502 is used to implement connection communication between these components.

[0048] Among them, the user interface 503 may include a display screen. Optionally, the user interface 503 may further include a standard wired interface and a wireless interface.

[0049] Among them, the network interface 504 may optionally include a standard wired interface and a wireless interface (such as a WI-FI interface).

[0050] This application also discloses a computer-readable storage medium, which stores multiple instructions adapted to be loaded by a processor to execute the above-mentioned high-frequency FBG sensor of a symmetric elliptical flexible hinge.

[0051] The above are only exemplary embodiments of the present disclosure and should not be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made in accordance with the teachings of the present disclosure still fall within the scope covered by the present disclosure.

[0052] This application aims to cover any variations, uses, or adaptive changes of the present disclosure, which follow the general principles of the present disclosure and include common general knowledge or conventional technical means in the technical field not recorded in the present disclosure. The description and embodiments are only regarded as exemplary, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A high-frequency FBG sensor for a symmetric elliptical flexible hinge, characterized in that, The high-frequency FBG sensor includes: an optical fiber Bragg grating, a base, a first elliptical flexible hinge, a second elliptical flexible hinge, a first mass block, and a second mass block; The left side of the base is connected to the first elliptical flexible hinge; the first elliptical flexible hinge is connected to the first mass block; The right side of the base is connected to the second elliptical flexible hinge; the second elliptical flexible hinge is connected to the second mass block; The optical fiber Bragg grating is arranged between the first mass block and the second mass block.

2. The high-frequency FBG sensor of a symmetric elliptical flexible hinge according to claim 1, characterized in that The base is a concave-shaped metal material, and the left side of the base and the right side of the base are symmetrical structures; the first elliptical flexible hinge and the second elliptical flexible hinge are arranged in the concave-shaped base.

3. The high-frequency FBG sensor of a symmetric elliptical flexible hinge according to claim 1, characterized in that, A first groove is arranged in the middle of the upper surface of the first mass block; A second groove is arranged in the middle of the upper surface of the second mass block; the first groove is aligned with the second groove; The optical fiber Bragg grating is arranged between the first groove and the second groove by means of two-point pasting.

4. The high-frequency FBG sensor of a symmetric elliptical flexible hinge according to claim 1, characterized in that, The base, the first elliptical flexible hinge, the second elliptical flexible hinge, the first mass block, and the second mass block adopt an integrated design and are completely symmetrical structures on the left and right.

5. The high-frequency FBG sensor of a symmetrical elliptical flexible hinge according to claim 1, characterized in that, The structural parameters of the first elliptical flexible hinge and the second elliptical flexible hinge are determined by a genetic algorithm; The structural parameters include: the long semi-axis b of the elliptical flexible hinge, the short semi-axis c of the elliptical flexible hinge, and the thickness t of the elliptical flexible hinge.

6. A monitoring method based on high-frequency FBG sensors, which is applied to the transformer application scenario and is implemented based on the high-frequency FBG sensor of a symmetric elliptical flexible hinge described in any one of claims 1-5, characterized in that The method includes: collecting the vibration signal of the transformer through the high-frequency FBG sensor with symmetrical elliptical flexible hinges; filtering the vibration signal to obtain a filtered spectrogram; performing time-frequency analysis on the filtered spectrogram to obtain the vibration data of each frequency component; constructing a machine learning model; obtaining a labeled transformer vibration signal data set; training the machine learning model through the labeled transformer vibration signal data set; inputting the vibration data of each frequency component into the trained machine learning model for classification and recognition to determine the operating state of the transformer and complete the monitoring of the transformer.

7. An electronic device, characterized in that, It includes a processor, a memory, a user interface, and a network interface. The memory is used to store instructions. The user interface and the network interface are used to communicate with other devices. The processor is used to execute the instructions stored in the memory so that the electronic device executes the method as claimed in claim 6.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions, and when the instructions are executed by a computer, the method as claimed in claim 6 is executed.

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